1. Field of the Invention
This invention relates to a camera for use with a film of a format having a row of perforations spaced in a lengthwise direction at alternate long and short intervals, in which each adjacent perforations at the long interval delimit one picture frame and each adjacent perforations at the short interval delimit an interval between each adjacent picture frames, and, more particularly, relates to a camera which automatically withdraw a filmstrip by one picture frame from a film cartridge at every exposure and rewinds the entirely, or even partly, exposed picture frames into the cartridge.
2. Description of Related Art
Photographic filmstrips formed with a row of perforations, two for each picture frame, have recently become well known. Typically, each two perforations are positioned beside the beginning and end of a picture frame, respectively, to delimit a picture frame to be exposed and each adjacent perforations besides each adjacent picture frames delimits an interval between the adjacent picture frames. Accordingly, the perforations are spaced in a lengthwise direction at alternate long and short intervals. The sum of the long and short intervals comprise an film movement distance for one picture frame. Such a photographic filmstrip is known from, for example, Japanese Unexamined Patent Publication No. 5-19368.
A film winding mechanism for a filmstrip of this format, which can be provided at relatively low cost, uses a sprocket with a pair of cogs on the outer periphery which are spaced at a distance matching the short intervals between the respective adjacent perforations and engage with the perforations. The film winding mechanism includes a motor which is activated in response to operation of a shutter release button to cause film movement by one picture frame which is followed by a full rotation of the sprocket. This film winding mechanism cooperates with a mechanism for automatically stopping film winding at completion of winding one picture frame and a motor control switch for starting and stopping the motor such that the film wind stopping mechanism is activated every time one frame film movement is completed to turn off the motor control switch, stopping the motor. The film winding mechanism of this type is comprised of a film wind stopping cam having a groove which is rotatable following rotation of the sprocket and a stopping lever. The stopping lever engages with the film wind stopping cam to stop the sprocket whenever the sprocket makes a full rotation, stopping film winding. By means of the rotation of the sprocket following film movement, the shutter drive mechanism is charged.
While the film wind stopping mechanism thus constructed have the ability to cause reliable one frame film movement by mechanically detecting the perforations, the shutter charging mechanism performs shutter charge in a period where the cogs of the sprocket remain engaged with the perforations, so that the mechanism is resistant to bias on the shutter applied by a strong charging spring.
With the film winding mechanism of this type, when a film rewind member is operated after completion of sequential exposures of the first to last picture frames, while the sprocket 27 is disconnected in operation from the film wind stopping mechanism and the shutter charging mechanism and enabled to rotate freely, the motor control switch is turned over to reverse the motor for rewinding the filmstrip. Because the sprocket has been rotatable freely, the exposed filmstrip is entirely rewound into the film cartridge without hinderance.
A recurring problem, however, is that since the sprocket is intermittently rotated by the filmstrip during being rewound, a position in which the sprocket stops when the film trailing end comes off the sprocket varies with variations in rewinding force of the filmstrip. Variations in stop position cause various problems. Specifically, if the sprocket has stopped with its cogs placed in the film path, a filmstrip at its leading end is caught by the cogs at the beginning of winding and hindered from being further wound. Even if the filmstrip is possibly wound, the film wind stopping mechanism is activated and stops the motor during winding the filmstrip.
Such a variation in stop position of the sprocket causes another problem in cases where the camera is equipped with a feature that the motor is automatically stopped after a specified margin time from shutter releasing in the event that film winding is disabled. During winding a filmstrip after the exposure of the last picture frame, the sprocket is not rotated by the trailing section of the filmstrip which is not provided with perforations, so that the film wind stopping mechanism is not activated, resulting in not turning off the motor control switch and allowing the motor continues to rotate in the forward direction. In order for the motor to automatically stop even when the film wind stopping mechanism is not activated, an electric timer which makes use of a discharging time of a condenser is incorporated to count a margin time, for instance 15 seconds, from shutter releasing in order to automatically stop the motor after the lapse of the margin time.
Assuming that the film rewind member is operated immediately after the exposure of the last picture frame to reverse the motor and restored after the filmstrip has been entirely rewound into the film cartridge, in cases where a filmstrip of a small number of exposures, for example 15 exposures, which takes only a short time to be completely rewound, is loaded, the electric timer has possibly not yet count the margin time when the film rewind member is restored. In this event, although the motor has been switched over to be ready for forward rotation, it is not activated even if the margin time has not yet passed. This is because restoring the film rewind member causes the film rewind stopping mechanism to operate to turn on a motor stop switch as long as the sprocket is in the proper stop position.
In cases where the sprocket stops in a position deviating from the proper stop position in which the film rewind stopping mechanism is caused to operate, if the eclectic timer has not yet counted the margin time, the motor starts to rotate in the forward direction to withdraw the filmstrip out of the film cartridge again.